Telephone-exchange system



arch 1a 1924. mama? G. A. E. LUNDELL TELEPHONE EXCHANGE SYSTEM Filed Nov. 14, 1919 I5 Sheets-Sheet l are?! 18 G. A. E. LUNDELL TELEPHONE EXCHANGE SYS TEM 3 Sheecs-Sheet 2 Filed Nov. 14 1919 Awe/7&9; ed/ye W580i lurid? March 18 1924.,

G. A. E. LUNDELL TELEPHONE EXCHANGE SYSTEM Filed Nov.

%\.fi /l 5% mv fiv Mia QNN Nu //7 van far 620/372 #zen [an/e ball Patented ar. 18, 1924.

GEORGE ALDEN E. LUNDELL, OF CHICAGO, ILLINOIS, ASSIGNOB TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

- GE SYSTEM.

ofiice, there being one telephone ofiice for-each grou It 15 one object of the present invention to provide asystem of trunking between such telephone ofiices by which the exchange system may be operated in a highly efficient manner.

Heretofore it has been the practice to operate such multi-oflice telephone systems over a call circuit or order wire, described on page 487 of McMeen and Millers Telephony edition of 1%}12. The call circuit or order wire according to the usual practice is a separate pair of conductors extending from one telephone oifice to another telephone office, and is employed exclusively by the o erators. When a subscriber originates a call, for example, the operator who answers him, commonly known as the subscribers or A operator, having obtained from him verthe desi ation of the' wanted subscri ers line epresses the call circuit or order wire key corresponding to the ofiice designation of the oflice in which the called line terminates. This key places her telephone set in operative connection over the order circuit to the telephone set of the trunk or B operator located ,at the trunk board in the wanted oflice. Upon hearing the numerical designation of a wanted line spoken, the trunk or B operator responds by verbally givin the number of an idle trunk'which she c ooses to use for the connection, each trunk terminatesin the B board in a lug, and the operator inserts into the multiple jack of the wanted subscriber, assuming, of course, that the wanted line is idle. The subscriber or A operator meanwhile connects by means of a well known cord pair the calling subscribers line and the trunk assigned forher use and the two subscfi'ibers are thus telephonically connecte According to the arrangement heretofore commonly em loyed in such s stems there are at each 0 the trunk boar s groups of groups of plugs are combined into one larger grou the same volume of trafic can be han ed with a reduced amount of apparatus. B providing a selector switch for each of t e trunks above referred to, and causing these switches to choose an idle plug, or switchboard, plugs can be placed in one common group and thus the number of plugs can be reduced without a reduction in the volume of traflic that they are capable of handling.

This separation of the. trunk from direct association with a plug makes it impracticable for the B operator to assi n the trunk number to the A operator as in t e operation above described; it has been necessary in trunking systems employing such traflic distributing switches to instruct the A 0 erators to manuall select an idle trunk. his they have done y touching the tip of-one ofvtheir plugs to the test thimble of the trunk jacks, a potential on the jacks of busy trunks causing clicks to be heard in the receiver. Since the operator may find it necessary to re eat this testing operation a lar e number 0 times where t e group of tr s is large such an arrangement is unsatisfactory and results in serious interference with the A operators work.

An object of the present invention is the selection of an idle trunk by means of a plurality of switches arran ed serially or in tandem whereby a single a lotter places them in operative relation to an idle trunk.

A further object of the present invention produces a simple and eflicient means of connecting a tele one trunk circuit to an idle plug in an id e operators position.

A further object of the present invention is the provision of a tone circuit whereby a.

- Fig. 1 re resents a part of the connection in the cal ing ethics and includes a primary line switch and a secondary switch; Fig. 2, which is to be placed immediately to the right of Fig. 1, represents the part of the system located in each called ofice, and includes a selector for joining the trunk and a plug; and Fig. 3, which is to be placed immediately below Fig. 1, represents a portion I of the apparatus located in the calling ofice,

and includes the master switch, the master switch bank, as well as an indicator trunk, and in skeleton form a second primary line switch and a second secondary switch for designating the selected trunk. Fig. 4 shows in detail the construction of the master switch bank. Fig. 5 is a chart indicating the relation of the principal units of the system, and shows diagrammatically the calling and called subscribers, and various ofiices of a multi-ofice telephone system.

The primary switch shown in Fig. 1, and Fig. 3, comprises a trunk finding apparatus, and for the purpose or" setting forth the invention I show a well mown line switch of the type described in British Patent 26,301 of 1900. Said line switch includes an electro-magnet 11, a plunger 12, a plunger shaft 13, of Fig. 1, and the master switch 301 of Fig. 3. The master switch 301 controls by the movement of the ratchet wheel 302 the plunger shaft 13, and a plurality of plunger as such as 12. Bank spring set 303 is a part of another bank spring set whose plunger arm (not shown) is operated by the same plunger shaft 13 as plunger arm 12. The master switch 301 is adapted to control ositionin of plunger shaft 13 to carry all me switc plungers opposite the next idle line in readiness to be seized on the next call. The ratchet wheel 302 also controls the movement of wiper 304 which in turn connects the conducting segment 305 to master switch bank contacts such as 300, 30?, 308, and 310. I

Ratchet wheel 302 is driven hy a motor meet 311 whose circuit is in turn controled by relay 312. The energization circuit for the relay 312 includes the wiper: 304, and whenever the said wiper 304 enes a bank contact having its guarding circuit closed through a low resistance path,

control relay 312 is caused to operate thereby energizing the motor; magnet 311, until the wiper 304 is steppedv into engagement with a bank contact having no low resistance guarding circuit. Included in the circuit of the w1 er 304 is the auxiliary relay 313 the function of which will be subsequently described.

Referring to Fig. 4, the master switch bank 314 comprises the individual contact oints such as 306, 307, 308, 310, separated lrom conducting segment 305 by insulating strip 401, and is so arranged that when the wiper 304 engages the last contact point 306, and then on its next step is carried to the contact point 310 on the right, the upper art of wiper 304 slides on spring 402.

his provision is made in order that the wiper 304 in passing from the extreme le'lt contact point 306 to the extreme right contact point 310 may not place contact points such as 307 and 308 in connection with the conducting segment 305 whereby some interference might be experienced by the master switch.

The secondary switch shown at 14 in Fig. 1, comprises a number of wipers 15, 10, 1'? and 18, which are caused, upon operation of stepping magnet 20, to step from one set of terminals, such as 21, 22, 23, and 24, into engagement with another set of terminals. such as those shown in line with terminal 25, in a well known manner. The terminals 21, 22, 2a, 2a, 25, 2c, 27, 2s, 30, an, 32, and. 33. are arran ed in tour circular rows in such manner t rat when the wipers 15, 10, 1?, and 18 are stepped from the last set of terminals these wipers are again positioned upon the first or normal set of terminals 21, 22, 23, and 24.

The secondary switch 14 is provided with a test relay 57 having a high resistance winding normally connected to the conductor 343 and to the master switch bank contact 307, The nesistanoe of the winding 0: 5 the test relay is sutliciently high to limit the current flowing in the following circuit when the wiper 304 contacts with the master switch contact 307, and this current is s'ut'- liciently low to prevent operation of relays 312 and 313, these relays being marginal: grounded battery 344, marginal relay 312, marginal relay 313, conducting segment 305 wiper 304, master switch bank contact 307,

conductor 343, contact 58, of relay 5?, winding oil-relay 57, conductor 60, wiper 13, terminal 24 to ground, it being assumed that the'trk of terminals 21, 22, 23, and 24 is busy, Relay 5?? is energized opening the contact 58, but the circuit of its winding is maintained energized nevertheless by way of front contact spring 01 and resistance 02 to grounded battery. A circuit "for stepping magnet 20 is now closed by way of grounded battery winding of stepping Elli are

magnet 20, contact 62 of stepping ma et 20, right hand front contact of relay 5 to ground, and the wipers 1.5, 16, 17, and 18 are caused in a well known manner to step away from terminals 21,22, 23, and 24, to the terminals in line with 25. The wiper 18 is so formed that it contacts with terminal before breaking contact with terminal 24, thus maintaining relay 57 energized while passing between terminals. I Assuming that terminal 25 is also grounded the stepping magnet 20 is again energized and the wipers are again moved, this time to the terminals in line with terminal26. As suming that this terminal is similarly grounded, the step in magnet 20 is once more energized an t e wipers 15, 16, 17, and 18, are now brought into engagement with the corresponding terminals 31, 30, 28, and 27. Assuming now that terminal 27 is ungrounded relay 57 is caused to release, and the stepping magnet 20 is deenergized thereby, causing the wipers to come to rest on the terminals mentioned.

This operation by means of which the selector 14 was caused to engage its wipers with terminals of an idle trunk, is a preselecting operation and occurs as a result of master switch wiper 304, having come into contact with the master switch bank contact 307 whose conductor 343 extended to the relay 57of selector 14. In Fig. 3

there is shown a part of ,a selector 814 cor responding to the selector 14, which has a similar stepping magnet 820, test relay 857, and conductor 843 associated with master switch bank; contact 308. So long as the wiper 304 does not contact wfith masterv switch contact 308 the test relay 857 and the selector 814 are notactive,.but as will hereinafter be described when the master switch wiper 304 is stepped into engagement with contact 308 this selector will be rendered active and will thereupon step its wipers, such as 818, into engagement with the terminal of an idle trunk.

The selector 201 of Fig. 2, comprises the wipers 202, 203, 204, 205, 206, and 20?,

adapted to be stepped by the operation of magnet 208 into engagement with a corresponding number of rows of terminals in a well known manner.' These wipers are arranged so that when they have been stepped away from the last terminals of the rows they are 'brought again into engagement with the first terminals or normal terminals shown in line with terminals 210, 211 and 212, The wipers 204 and 205 are so formed that they contact with terminals at all times whereby the circuit remains unbroken while they pass between terminals.

The wipers 704, 705 and 706 are part of another selector 701 and correspond to also mounted on the constantly driven shaft mentioned, and coacts with contact spring- 321 to close a circuit to conductor 331, as will be more fully described below.

The registering switch 332 comprises wipers 333 and 334 controlled by stepping magnet 335 whereby said wipers 333 and 334 are caused to be moved over the rows of terminals 336 and 337 in a well known manner. The rows of terminals 336 and 337 are so disposed that when wipers 333 and 334 are stepped away from the last terminals 38 and 340, they are at once returned to the normal positions 341 and 342..

The subscriber at station 1, Fig. v1, desirmg to originate a telephone call to subscriber 213, of Fig. 2, removes his receiver and closes thereby a circuit extending from grounded battery 2 to winding of relay 3, contact 4, of relay 5, conductor 6, substation 1, conductor 7, contact 8 of relay 5, to ground, ener izing thereby relay 3 closing the circuit 0 line lam 10. The subscribers operator u on noticing that line lamp 10 is lighted c ooses a plug 34 of one of those in her position which are. not at the moment engaged, and inserts it into jack 35 establishin thereby a circuit from the grounded attery 36 through supervisory signal 37, resistance 38, plug 34, jack .35, cut ofi relay 5 to ground, operating relay 5 which opens contacts 4 and 8. This causes station transmitter and for operating relay 42. The operation of relay 42 closes at its front contact a shunt circuit by way of conductor 43, and resistance 44 around supervisory lamp 37. The resistance 44 is of such value as to reduce the current through supervisory lamp 37 sufliciently to dim it to the point where its illumination will not be noticeable to the o erator. The 0 erator now closes listening ey 45 and estab ishes a telephone'connection from her telephone set 46 to the right hand windings of repeating coil 41, and thus inductively to the calling subscribers. She ascertains over this circuit verbally the number of the subscriber wanted.

The-subscribers operator now closes the key 47 and establishes a circuit through contact 48 for operating relay 50, as well as a circuit closed at contact 51 for starting a trunk finding operation which will now be described in detail.

The plunger 12 of the primary switch, as described in British Patent 26,301, of 1906, always stands before the set of springs asso ciated with an idle line. closed from grounded battery'345, back con tact of relay 313, conductor'346, contact 65, right handwinding of electroinagnet 11, conductor 348, contact 51' of key 47' to ground; This energizes electromagnet 11 and the plunger 12 is drawn forward forcing the insulatingball' 52 thereof between the innermost springs of the set, whereby each of the four springs is forced outwardly into engagement with its cooperating contact.

The closure of contact 53 causes the operation of relay 54 over the following circuit: grounded battery 55, winding of relay 54, conductor 56, contact 53 to ground. I The operation of relay 54, closes at its'left" hand front contact a "low resistance path from ground over "conductor 343" to the master switch contact 307, whereby all of the remaining I idle plungers of the primary switches are moved to a position before the springs, and associated with the next idle -The following circuit isthen closed: the grounded battery 344, winding of marginal relay 312, winding of marginal relay 313, conducting segment 305, master switch wiper 304, master switch bank contact 308, conductor 843, contact 858 of relay 8'57, whereby selector-814 is rendered active, and its'wipers are caused to he stepped into engagement-with an idle trunk. "lhe operation of selector 8-14 and ofrelay 857 is similar to that of selector 14 and relay 57-described above.

The operation of relay 54 alsocloses a ground connection from the right hand back contact of relay 57, conductor 105, contact 104' of relay 54,'wiper'18, contact 27 to comeoluctor 103. 'lhis ground-connection'to the test conductors such as 103 and-the test terminals such as 27 prevents other switches such as 814 corresponding to the selector 14 from establishing connection with thesame trunk.

It will thus be seen that the master switch 301 of the primary switch preselects' or allots, before each call, the "trunk or line 74,

1 86 next tobe used, extending to the selector 14 Upon such per-selection the selector l4 is rendered'active, and steps'its wipers into electromagnet 11 is held in its actuated position independent of the opening of contacts 347and 65.

Relay 66 is now energized over a circuit from grounded battery, winding of relay 66 conductor 67, contact 68 of relay 57, con ductor 56, contact 53 to ground. A circuit is now closed from grounded battery 70, left hand winding of relay 71, conductor 72, contact 73, conductor-74, contact 75 of relay 66, conductor 76, wiper 16, terminal 30, conductor 77, contact 81, conductor 78, lower left winding of repeating coil 214 of Fig. 2,conductor 215, left hand winding. of relay 216, conductor 217,'upper left hand windingjof repeating coil 114, conductor 80, contact 82, conductor 83, terminal 28, wiper 17, conductor 84, contact 85 0f relay 66, con ductor 86, contact 87, conductor 88 through the ri ht hand winding of relay 71 to groun Relaysi'l and 216 operate. Relay 71 connects at its left hand, front contact a ground connectionv in multiple with the contact 48, key'47 and the operator ma now remoive' her finger from this key,

eferring to Fig. 2 the operation of relay 216 closes a circuit from grounded battery 218, winding of relay 220, front contact of relay '216, conductor 221, contact 222 of relay 223 to ground, operating relay 220. The relay 220 closes at its left hand front contact a ground connection in multiple with the conductor 221, contact 222, whereby relay 220 is held energized independent of said contact 222. Relay 220 also closes at its right/frontcontact a circuit from the grounded battery 224 through the left hand winding of relay 223, a conductor 225, terminal 211, wiper 206, conductor 226,

right hand front contact of relay 220 to ground. Relay'223 thereupon operates and establishes a locking circuit for itselffrom ground 227, wiper 204, conductor 228, contact 230, right hand winding of relay 223 to grounded battery 224. Relay 223 also closes at its left hand front contact a circuit from the grounded battery 231, step ping magnet 208 of selector 201, the contact 232 of this magnet, conductor 233, left hand' front contact of relay 223 to ground. The operation of stepping magnet 208 causes advancement of wipers 202, 203, 204-, 205 206, 207 over the rows of terminals in a well knownman'ner. A. circuit is also closed from grounded battery 234, winding of relay 235, conductors 236 and 233, left hand front contact of relay 223 to ground, and the operation of relay 235 opens at contacts 237 and 238 the circuits of wipers 202 and 203- during the advancement of these wipers over their respective terminals. Test circuit for selector 201 is a multiple test circuit having a branch by way of contact 240, conductor 24f, wiper 205, for testing sets of terminals in groups, and another branch by way of contact 230, conductor 228, wiper 204, for testing the sets of terminals individually. The release of relay 223 is dependent upon both the wipers 204 and 205 contacting with ungrounded terminals, and this requires that the group as well as the individual terminal be idle. The plug with which terminal 242is connected is assumed to be busy and 'the ground con.- nection therefore exists for thisterminal by way of conductor 743, wiper 704, contact- 744 of relay 723, conductor segment 746, wiper 706, conductor 726, right hand front contact of relay 720 to ground. The nu merals 701 and other numerals in 700 designate parts which correspond to similarly numbered'parts in the 200 series.

The plugs 252 which may be selected by the selector 214 are preferably arranged in groups before operators positions. For instance, if th switch 214 is provided with twenty sets of contacts, ten of these con-' tacts may be wired to plugs at one operators position and the remaining ten ma be wired to plugs at a second operators position. The number of groups and the number of plugs at each position would vary in accordance with the capacity of the switch. 214, which may of course, be made of any desired size.

It is obviously advantageous to select not only an idle plug, but a plug at an idle operators position, in order that calls may be handled as'expeditiously as possible.

Inasmuch as the switch is provided with a special testing circuit described hereinafter, whereby at each step a test is made as to whetherthe plug is idle and whether the group in which such plug is located is idle, the contact setsanay be arranged in any desired order in the contact bank. It is of course, immaterial whether the switch hunts through all the contacts leading to plugs in one group and then begins hunting in a second group, or whether it tests a contact set leading to a plug in one group, and then tests a contact set leading to a plug in a different group. The multiple connections to conductors 250 and 243 m dicate which contacts are assigned to plugs at the operators position shown. The lousy or idle condition. of the group is controlled by relay 247 at the position shown and by relay 747 corresponding thereto at another position.

The continuedenergization of relay 223-as a result of the closure of the plug testing circuit described causes the stepping magnet 208 to continue the movement of the wipers,- and the latter are accordingly brought into contact With the third row of terminals.

lit is assumed that the group with which the plug ccnnected to the'third row of tarminals helongs is busy and that relay 747, corresponding to relay 247 is operated. The

'tion to relay 247 for another manner of operating these last mentioned relays will be subsequently set forth. Assumingthat relay 747 is in its operated position a circuit for the continuedenergization of test relay 223 is closed as follows: grounded battery 224, right hand winding of relay 223, contact 240 of this relay, conductor 241, wiper 205, conductor 248, front contact of relay 747 to ground. Stepping magnet 208 therefor is again energized over the circuit: grounded battery 231, winding of stepping magnet 208, contact 232 of'this magnet, conductor 233, left hand front contact of test relay 223 to ground, and stepping magnet 208 steps the wipers from the third row of terminals to the fourth row of terminals, and it is assumed that theplug with which this 'rowof terminal-s is associated, and the group to which the plug belongs are idle, and that no ground exists on conductors 243 and 250.

Test relay 223 releases and stepping magnet 208 consequently remains deenerg'ized. Relay 235 now releases. A ground connec-v tion is now established from ground to right hand front contact of relay 220, the conductor 226, wiper 206, conducting segment 246, conductor 245, contact 244 of test relay 223, conductor 228, wiper 204, conductor 643, extending to other switchescorresponding to 201 whereb an of these other switches which may test t e circuit of plug 252 will be advanced from engagement with the row of terminals towhich conductors 753, 754,

643 and 750 extend. The same ground closes a circuit over conductor 243, left hand back contact of relay 251, conductor 255, relay 256, conductor 257 and relay 247 to grounded battery, operating relays 247 and 256. The operation of relay 247 connects a ground-to conductors 250 and 750, whereby other selector switches corresponding to selector 201' when testing the terminal connected with conductor 7 50 may find a ground for holding energized the test relay and consequently for'advancing such selector switch from the row of terminals to Which conductor 750 is connected. Relay 747 corresponds in funcroup, and Y the operating circuit of relay 74 is similar to that just described for relay 247.

The operation ofrelay 256 closes a circuit from grounded battery 258 through lamp 260, conductor-261, right hand front contact of relay 256, to ground whereby the lamp 260 is illuminated, indicating that there-is a call waiting on the associated plug 252. The operation of relay 256also operati vely connects the telephone set 262 by way of its contacts 263 and 264, and wipers 2'02 and 203 to the right hand windings of rcpeating coil 214 and thereby to the trunk.

-A complete order circuit is now established from the A operators telephone set .46 to the B operators telephone set 262 as follows: the A operators telephone set 46,

conductor 90, right hand front contact of relay 50, which is in its operated position, conductor 72, contact 73 of the primary line switch, conductor 74, front contact 75 of relay 66, conductor 76, wiper 16, contact 30 of selector 14, conductor 77, contact 81 of relay 91, conductor 78, lower left winding of repeating coil 214, condenser 265, upper left winding of repeating coil 214, conductor I 80, contact 82 of relay 91, conductor 83, terminal 28, wiper 17, conductor 84, front contact 85 of relay 66, conductor 86, contact 87, left hand front contact of relay 50, conductor 92, condenser 93 to the operators telephone set 46. Inductively associated with the left hand windings of repeating coil 214, mentioned, are the right hand windings thereof, and a circuit extends from grounded battery 266, lower right winding of repeating coil 214, winding of relay 267, contact 238 of relay 235, wiper 203, conductor 254, front contact 263 of relay 256, condenser 268,; secondary winding of induction coil 270, head receiver 271, conductor 272, front contact 264 of relay 256,

conductor 253, wiper 202, con-tact 237 of relay 235, upper right winding of repeating coil 214 to ground. The A operator gives verbally over this conversational circuit the numerical designation of the wanted line. It is, of course, unnecessary for her to give the ofice designation since her selection of key 47 caused a trunk to the selected office to become connected with her telephone set. The B operator need make no acknowledgment and the illumination of the lamp 260 being located for convenience near its correspondin plug 252, indicates to her the plug whic she should employ. The two operators now proceed to set up the connection, each doing her work independentlyand simultaneously. A detailed description of the A operators work will first be given,

and subsequently the work of the B operator will be described.

The A operator becomes apprised of the designation of the trunk over which the above described order circuit was completed in the following manner. The operation of relay 71 previously described closes a circuit from ground through right hand front contact of relay 71, conductor 351, winding of relay 352 to grounded battery, operating relay 352. A circuit is now closed from.

ground through the right hand front contact of relay 352, conductor 353, right hand back contact of relay 354, conductor 355, winding of relay 356, left hand back contact of this relay, conductor 331, contact spring 321 to grounded battery 357, when the contact spring 321 is caused to be operated during the rotation of the cam 315; Cam spring 321 is closed only at the beginning of a cycle, and remains closed for an interval long enough to operate relays of type shown at 356 and 354. ll prefer to use a cam 315 which closes the contact 321 during an interval of about twenty thousandths of a second, but any suitable cam may be employed. The operation of relay 356 in the circuit described, closes at its left hand front contact a circuit from grounded battery 358 independent of the contact 321. Constantly driven cams 316, 317, 318, and 320, coact with battery 357 and contact springs 322, 323, 324, and 325, to produce in oonductors'326, 327, 328 and 330 variously characterized currents.

The constantly driven cam 320is arranged to close the contact spring 325 nine times during each revolution, and during each of these closures the following circuit is completed: grounded battery 357, the contact spring 325, the conductor 330, terminal 31, wiper 15 of selector 14, conductor 94, contact 95, conductor 360,'right hand front con- 'tact of relay 356, winding of relay 361 to ground. During such revolution of the cam 320, relay 361 is accordingly operated and released nine times. Stepping magnet 335 in local circuit with the contact 362 of the relay 361 is operated nine times,'and in a well known manner advances the wipers 333 and 334 over the terminal arcs 336 and 337 respectively nine steps. After one complete revolution of the cams 315 and 320, the cam 315 again causes contact spring 321 to be closed and a circuit is now closed as follows: grounded battery 357, contact spring 321, conductor 331, left hand back contact of re lay 354, windingof this relay, conductor 363, left hand front contact of relay 352, conductor 364, ninth terminal of the are 337, wiper 334, to ground,,operating the relay 354. A circuit from grounded battery 365 isclosed through the left hand contact of the relay 354 maintaining this relay energized independent of the contact 321. The operation of relay 354 breaks a circuit described above over conductor 355 to the winding of relay 356, which thereupon releases and opens at its right hand front contact the circuit of relay 361 which themupon releases. ()peration of relay 354 also closes an indicator circuit from grounded battery 366, indicator lamp 367, conductor 368, ninth terminal of the are 336, wiper 333, right hand front contact of relay 354, conductor 353, right hand front contact of relay 352 to The lamps 367,370, and 371,- form part of an indicator setin accordance with the characteristic current applied to the terminal such as 31, associated with the trunk selected by the selector-'14. For .the purpose of illustration the terminals 32. and 33 have been shown connected by way of conductors 327 and 326, connected to the camsprings 323 and 322. Had the terminals 27, -28, 30, and 31, been busy at the time selector switch 14 ground, lighting the lamp 367.

lltl

was employed in setting up the connection described, in the manner set forth for busy terminals 25 and 26, and had the wipers 18, 17, '16, and 15, consequently been advanced in the manner described to the terminals associated with terminal 32, the selecting relay 361 would have been operated under the control of cam spring 323 and stepping magnet 335 would have advanced the wipers 333 and 334 five steps, so that the vindicator lamp 370 would have been lighted, and similarly had the terminal 32 also. been found busy, and consequently the wipers stepped intoassociation with the terminal 33, the.

cam spring 322 would have been em loyed and the stepping magnet 335 woul have operated only once, the wipers 333 and 334 would have been advanced only one step, and the indicator lamp 371 would have. been operated. In this manner the indicator lamps 367, 370, and 371 are responsive to the characteristic currents foundon the terminals such as 31, 32, and 33, associated withthe trunk which is used as the order circuit.

The lighting of the indicator lam apprises the A operator of the designatlon of the trunk used for the connection, and she inserts the plug 96 into the jack 97, bearing thatdesignation. A circuit is now established from battery 98 through supervisory lamp 100, resistance 101, plug 96, jack 97, winding of relay 91 to ground, lighting lamp 100 and operating relay 91. Relay 91 Y closes at the contact 102 a ground connection to conductor 103, whereby the terminal 27 is held busy independent of the ground connection through the contact 104 and conductor 105.

A circuit is now established from grounded battery 40, lower right hand winding of repeating coil 41, the winding of marglnal supervisory relay 106, plug 96, jack 97, contact 107 of relay 91, trunk line conductor 78, lower left winding of repeating coil 214, conductor 215, left hand winding of relay 216, and conductor 217, upper left winding of repeating coil 214, trunk line conductor 80, contact 108 of relay 91, jack 97, plug 96, conductor 110, upper right winding of repeating coil 41 to ground, thereby providing a circuit for holding the relay 216 energized independent of the battery supply hitherto received through the relay 7]." The left hand winding of relay 216 is of high resistance and the current in this circuit is insufficient to 0 rate the marginal relay 106.

It will e seen that the A operator can insert plug 96 into jack 97 as soon as she has spoken the number of a wanted subscriber, and as soon as the indicator lamp such as 367 has lighted, and that the relay 216 is held energized equally well from the battery 40 or from the battery 70.

The opening of contacts 81 and 82 of relay 91, breaks the circuit of relay 71 preintermittently operated, and carries the wipers 333 and 334 back to the normal position in engagement with contacts 341 and 342. The indicator is thus made ready for a new call. The opening of the left hand front contact of relay 71 opens the circuit of relay 50 and electromagnet 11. The plunger 12 of electromagnet 11 is released and the insulating ball 52 is withdrawn from the innermost springs of the bank set. Contacts 53, 73, 87, and 95 are thereby opened. The opening of contact 53 releases the relays. 54 and 66. The opening of the left hand front contact of relay 54 removes the low resistance ground connection to the master switch bank contact 307, thus rendering this contact available for use on a subsequent call. The opening of contact 104 of relay 54 disconnects the direct ground connection from right hand armature and back contact of relay 57, conductor 105, contact 104 of relay 54 to the wiper 18, but the terminal 27 is still provided with the direct ground connection by way of conductor 103 and contact 102 of the relay 91. I

The A operators telephone set is thus disconnected from the selected trunk, and she may now respond to another call.

The B operator icks up a plug 252 associated with the lig lited lamp 260, and tests the called subscribers line in the well known manner. Assuming that the called line is idle she inserts the plug 252 into the jack 273 of the called line. A circuit is now closed from grounded battery 274, winding of relay 275, plug 252, jack 273, conductor 276, and winding of cut off rela 277,- to ground, operating relay 275 and disconnecting the busy test lead from the plug 252.

A circuit is now established from grounded battery winding of relay 251, lower front contact of relay 275. winding of relay 278 to ground, operating relays 251 and 278. The operation of the relay 251 opens the circuit to conductor 255 and releases relays 256 and 247. The release of relay 247 disconnects ground from conductors 250 and 750 and permits the group of plugs associated with relay 247, that is with the operators osition, to be used 'on a subsequent call.

he release of relay 256 extinguishes the lamp 260 and also disconnects the operators telephone set 262 from the circuit.

As soon as relay 251'closes its left hand front contact a direct ground from the right hand front contact of relay 220, conductor 226, wiper 206, conducting segment 246, com ductor 245, contact 244 of relay 223, conductor 228, wiper 204, conductor 243 is applied to conductor 280, whereby relay 278 becomes short circuited. Relay 278 is a slow pull up relay and does not respond to a short impulse of current flowing through its winding. lhe same ground is also effective for locking relay 251 independent of the lower front contact of relay 275.

A circuit is now closed from grounded battery, winding of rela 281, back contacts of relays 282 and 283 an 27 8, plug 252, jack 273, conductor 276, winding of relay 277 to ground, energizing relay 281. This relay impresses upon the called subscribers line ringing current from a source 284 through the winding of relay 283, left hand front contact of relay 281; plug 252, jack 27 3, substation 213, jack 273, plug 252, upper front contact of relay 275, right hand front contact of relay 281, to ground, causing the substation bell to be operated. Relay 283 is marginal and does not operate upon current through the condenser and ringer of the substation set 213. Response of the called subscriber connects into circuit a. low resistance through his substation transmit ter, and thereby increases the current flowing in this circuit 'sufiiciently to operate relay 283. The operation of relay 283 removes a shortcircuit from around the Winding of relay 282, and this relay operates in the circuit: grounded battery, winding of relays 281 and 282, back contact of relay 278, plug 252, jack 273, conductor 276, winding of relay 277 to ground. Relay 282 connects at its front contact a circuit from the same grounded battery to the winding of relay 282, whereby the winding of relay 281 becomes short circuited. Relay 281 retracts its armature and closes a conversational circuit from grounded battery 266 through lower right winding of repeating coil 214, winding of relay 267, contact 238 of relay 235, wiper 203, conductor 254, left hand back contact of relay 281, plug 252, jack 273, called subscribers substation set, jack 273, plug 252, upper front contact of relay 275, right hand back contact of relay 281, conductor 253, wiper 202, contact 237 of relay 235, upper right winding of repeatingcoil 214 to ground. The right hand windings of repeating coil 214 are inductively related to the left hand windings and this conversational circuit is thereby extended over trunk line conductors 78 and 80 through the repeating coil 41 to the calling subscribers set, whereby the two subscribers may carry on their conversation.

The operation of relay 267 closes the circuit' of the low resistance right hand winding of relay 216 in parallel with high resist ance left hand winding of this relay and increases thereby the current in the circuit of relay 106, sufliciently to operate said relay 106. A shunt circuit through resistance coil 111 is therefore laced around a supervisory lamp 100 causing it to be dimmed.

Upon the completion of conversation the subscribers 1 and 213 replace their receivers, thereby retracting the armatures of relays 42, 267 and 106, and causing lamps 37 and 100 to burn brightly in the circuits which have been fully described above. The A. operator thereupon disconnects the plug 34 from the jack 35, thereby extinguishing the lamp 37 and releasing the cut off relay 5, and also disconnects the plug 96 from the jack 97, thereby extinguishing the lamp 100 and releasing relay 91. The release of relay 91 removes the ground connection by way of contact 102, whereby the trunk line conductors 78 and 80 are caused to test idle to such selectors as 14 and 814:.

As soon as plug 96 is removed from the jack 97, the circuitof relay 216 is broken, and this relay is released, whereupon relay 220 in turn is deenergized. A circuit is now closed from grounded right hand back contact of relay 220, wiper 207, conducting segment 285, conductor 225 to the left hand winding of relay 223and grounded battery 224. Relay 223 is operated and opens contact 222, whereby subsequent operation of relay 220 is prevented until selector 201 reaches its normal position. The selector magnet 208 is energized in a circuit from grounded battery 231, winding of stepping magnet 208, back contact 232 of this magnet, conductor 233, left hand front contact of relay 223 to ground. Intermittent operation of the stepping magnet 208 under con trol of its contact 232 steps the wipers 202, 203, 204, 205, 206, and 207 until'these wipers have left the last row of terminals and have reached the normal position. Upon reaching the normal position, the circuit from wiper 207 to conducting segment 285 and relay 223 is released, whereby further operation of stepping magnet 208 is prevented. During the advancement of the wipers relay 235 becomes energized in a circuit extending from grounded battery 234, winding of relay 235, conductors 236 and 233, left hand contact of relay 223, to

ground. and the circuit of wipers'202 and 203 is held open at contacts 237 and 238 during the movement of such wipers. The relay 235 releases as soon as the selector reaches normal, 'its circuit being broken upon the release of relay 223.

Breaking of the ground connection from the right hand front contact of relay 220 removes the short circuit previously described from around relay 278, and this relay now operates in a circuit from grounded battery, the windingof relay 251,

conductor 280, lower front contact of relay 275, winding'of relay 278, to ground. The operation of relay 278 opens at its upper back contact the circuit of relays 281 and 282, rendering such relays ineffective. Relay 278 closes at its lower front contact the circuit of disconnect lamp 286. and the resulting illumination of this lamp indicates to the B operator that she should disconnect plug 252. Upon her doing so the circuit of relay 275 is broken, and this in turn opens the circuit of relays 251 and 278, and extinguishes lamp 286. It will benoted that until the operator disconnects plug 275 a ground connection extends to conductors 243 and 643, by way of the left hand front contact of relav 251, conductor 280, lower front contact of relay 275, winding of relay 278, whereby such switches as 201 and,l0l"'vvhose wipers 204, 704, contact withtlie conductors 243, 743 while testing will' 'be cau sed to step away from the associatedterininals.

Should the B operator inadvertently disconnect the plug 252, from the jack 273, while the subscribers 1 and 213 are engaged in conversation, relay 27 5 will retract its armature and a circuit will be closed from grounded battery, pulsator 287, resistance 288 right hand front contact of relay 251, lower back contact of relay 27 5, winding of relay 27 8, to ground. Relay 278 Willthereupon be intermittently operated, and the lamp 286 will flash, indicating to the operator that she has made a mistake.

Fig. 5 shows the arrangement of the various circuits and apparatus. of a telephone exchange system according to the present invention, and shows at 1 the subscribers station 1 of Fig. 1. 502 is a diagrammatic representation of the connecting apparatus of the A operators position one of which is also shown in Fig. 1. 213, 511, 512, 506, 507, and 508, represent called subscribers stations arranged in two groups. the group comprising stations 213. 511 and 512, being adapted to be connected to by plugs such as 252, 513, 514. vThese stations are wired according to the diagram at the right of Fig. 2. The selectors 201 and 701 are arranged to seize an idle one of such plugs.

Similarly subscribers stations 506, 507, and 508, are adapted to be connected to by plugs such as 516, and these in turn may be selected by switches such as 517, 518. Plugs 513, 514, and 516 are wired similarly 'to 252, as shown in Fig. 2. and the selectors 701, 517, and 518, are wired similarly to the selector 201, as shown in Fig. 2. As has been described in detail, the selector 14 and the line switch 12 cause the selection of a trunksuch as 78 or 520 extending from the A office 502 to selectors 201 or 7 O1.- The indicator 367 is operated in accordance with the setting of switch 14, as previously described,

to indicate to the A operator the numerical designation of the'trunk to which the automatic switches have, made connection. whereby she may establish connection to the same trunk by means of one of the connecting apparatuses 502. Another key 547is provided for causing the operation of additional switches similar to 12, 14, in order to select a trunk extending to selectors 517 518 located in the oflice in which subscribers lines 506, 507, and 508 terminate, and the operation of the system on such a call is in all respects similar to the case described.

Should the A operator depress the key 47 during the period when the selector 14 is active, and the stepping magnet is intermittently operating, a tone will be heard by the operator in her telephone set 46 due to the connection through the condenser 112. This condenser is discharged and charged by the closing and openingof contact 62 while the selector 14 is in active operation and the potential upon the conductor 88 is thereupon caused to vary. This varying potential causes a varying current to be induced in the following circuit: grounded battery 70, left-hand winding of relay 71 right hand front contact of relay 50, conductor 90, telephone set 46, condenser 93, conductor 92, left hand front contact of relay 50, righthand winding of relay 71 to ground. The buzzing tone produced in the telephone set 46 lndicates to the A operator that an idle trunk is not at the moment available. The tone continues so long as she holds the key 47 pressed, and so long as the selector 14 continues stepping over busy trunks. When the selector 14 contacts with the terminals of an idle trunk, as previously described, the test relay 57 releases, the relay 66 operates, and the tone circuit is broken. The operator then knows by the discontinuation of the tone that she mayproceed to set up the call in the manner described above.

I claim as my invention:

1. In a telephone exchange system a plurality of trunks, an operators telephone set, automatic selecting mechanism adapted to connect said operators'set to an idle trunk. and a variably operable device for indicating the designation of said trunk.

2. In a telephone exchange system a plurality of trunks, an operators telephone set, automatic selecting mechanism having a receiving position for each of said trunks adapted to connect said operators set to an idle trunk, and a variably operable device for indicating the designation of said trunk. I

3. In a telephone exchange system, an automatic selector including a contact bank,

cups of lines terminating in said contact ank, a test'relay, a multiple circuit for said relay, means to extend one branch of said circuit to a contact, means to control the electrical condition of said contact in accordance with the busy or idle condition of said line, means to extend the other branch of said circuit to another contact, means to control the electrical condition of said other contact in accordance with the busy or idle condition of a group of lines, and means to operate said test relay under the control of said multiple circuit.

4. In a telephone exchange system a series of trunk selecting switches arranged sequentially, and allotting mechanism for one of said switches adapted to render a subsequent switch active.

5. In a telephone exchange system means for preselecting an idle trunk line, a selector in which said trunk line. terminates, and means operable upon such preselection to render said selector active.

6. In combination in a telephone exchange, a telephone set, a plurality of trunks, an automatic selector for connecting said telephone set with any of said trunks adapted to be advanced over busy trunks, a stepping magnet for said switch, and means controlled by saidmagnet for impressing upon said telephone set a tone durmg such advancement.

7. In a telephone exchange system a plurality of trunks, an operators telephone set, automatic selecting mechanism adapted to connect said operators Set to an idle trunk,

and a numerical indicator set in accordance with such trunk selector.

8. In a telephone exchange system a plurality of trunks, a source of variously characterized currents, an operators telephone set, automatic selecting means adapted to connect said opra'tors set to an idle trunk, an indicator, and means responsive to said variously characterized currents for controlling said indicator.

9. In a telephone exchange system a plurality of trunks, an operators telephone set, automatic trunk selecting mechanism adapted to connect said operators set to an idle trunk, an indicator and a source of variously characterized currents adapted to'control the setting of said indicator according to the setting of said mechanism.

10. In a telephone exchange system a line switch, a master switch, means controlled by said master switch for positioning. said line switch, a secondary switch, and a test circuit for said secondary switch, including contacts of said master switch.

11. In a telephone exchange system, an A. operators position, a plurality of B operators positions, telephone sets for said operators, circuits at said positions, and means responsive to the electrical conditions of said circuits to automatically extend the connections of said A. operators telephone set to the telephone set of an idle B operator.

12. In a telephone exchange system, an A operators position, a plurality of B operators positions, telephone sets for said operators, circuits at said positions, trunk lines extending from said A operators position to-said B operators positions, and means responsive to the electrical conditions of said circuits and trunk lines to automatically extend the connection of said A operators telephone set to an idle trunk line and thence to the telephone set of an idle B operator.

13. In a telephone exchange system, an A. operators position, a plurality of B operators positions, cord circuits at said positions, trunk lines extending from said A operators position to said B operators positions, a telephone set for said A operator, and means responsive to the electrical conditions of said circuits and trunk lines to automatically extend the connections of said telephone set to an idle trunk line and thence to an idle cord circuit at an idle B operators position.

14. In a telephone exchange system, an A. operators position, a plurality of B operators positions, cord circuits at said positions, telephone sets for said operators, trunk lines extending from said A operators position to said 13 operators positions, an automatic switching device to extend the circuit of said A operators telephone set to an idle trunk line, a second automatic switch to extend said connection from said trunk line to an idle cord circuit at an idle B operators position, and means to extend connection from said last mentioned cord circuit to the telephone set of the B operator whose position has been selected.

15. In a telephone exchange system, an incoming line, an A operators position, a B operators position, cord. circuits at said positions, a trunk line extendin from said A operators position to said fi operators position, telephone sets for said operators, automatic means to establishconnection from said A operators telephone set to said B operators telephone set, means to indicate the number of the trunk circuit used, and means including a cord circuit to enable the A operator to extend said incoming line to the selected trunk.

In testimony whereof, I hereunto set my hand.

GEORGE ALBEN E. LUNDELL. 

